In image capturing systems involving the lenses such as the one shown in FIG. 1 of the drawings, the light distribution by the lens system is non-uniform, causing a captured image to have some light intensity fall-off toward the edges of the image. This artifact is called the lens shading artifact or vignette. FIG. 2 of the drawings illustrates the effect of the lens shading artifact on a captured image. Referring to FIG. 2, it will be seen that a captured image 10 includes a central circular region 12. Light intensity is brightest at the center of the circular region 12 and falls off radially away from the center. Edges 14 at the corners at the image 10 show the greatest fall off in light intensity.
The lens shading artifact may be removed by multiplying the light intensity I(x,y) at the image location (x,y) by a lens shading correction amount L(x,y)Icorrected(x,y)=I(x,y)×L(x,y)  (1)
In reality, for image capturing systems that include an image sensor, the sensor might contribute offset terms that would make the Equation (1) more complex. The offset terms are not considered so as to not to obscure the invention. However, one skilled in the art will know how to modify Equation (1) with the offset terms.
In one technique to correct for the lens shading artifact known to the inventor, the lens shading artifact is modeled so that the function L(x,y) may be inferred from the model. In another technique to correct for the lens shading artifact, the function L(x,y) is directly measured and calculated. With both these techniques, the function L(x,y) is a two dimensional (2D) function that depends on both x and y coordinates.